Why is my dog shivering?

Common reasons a puppy shivers: cold, fear, excitement, or illness. When the ambient temperature is low, a dog shivers to resist the cold; if the temperature is fine, rule this out. Second, a dog shivers when stimulated, frightened, nervous, anxious, or insecure. Also, a dog shivers when excited — e.g., meeting its owner or a friend after a long time. In addition, a sick dog may shiver from epilepsy or neuromuscular disease or distemper. If shivering lasts long or recurs often, take the dog to a vet promptly.